System and methods for recording a compressed video and audio stream

ABSTRACT

A system for recording a compressed video-audio stream includes a decoder for decoding the video and audio packets of the stream, a multimedia recorder for recording the video and audio portions of the stream, and a video frame editor. In one embodiment the multimedia recorder receives and ignores initial delta frames of the video portion of the stream while buffering the audio portion of the stream received until a first key frame arrives and is buffered and decoded and wherein upon receiving a command to record, the system writes a copy of the key frame at a predefined interval the first interval corresponding with the start of the recording of the audio portions of the stream, the write interval repeated successively until a next key frame arrives whereby the video and audio is then recorded as received.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is in the field of digital video and audiorecording and pertains particularly to methods and apparatus forrecording live, compressed video and audio streams.

2. Discussion of the State of the Art

In the art of video and audio transmission, video and audio data aremost often stored and transmitted in a compressed format to savebandwidth. A typical method of video compression Moving Pictures ExpertsGroup (MPEG) involves storing and transmitting only some of the fulldata video frames of the video-audio stream. A full video frame may bereferred to as a key frame known in MPEG compression format as anintra-coded pictures frame (I-frame). Delta frames are video frames thatcome before and after a key frame. Delta frames are known as predicted(P) frames and bidirectional (B) frames in the compression format thatdefines the I-frame. For example, in a scene where a car moves across astationary background, only the car's movements will be stored in thedelta frames. P frames generally follow an i-frame and contain onlyvideo data that has changed from the preceding i-frame. P-frames rely onthe preceding i-frame for the rest of the video data. B frames containonly data that has changed from a preceding frame or data that isdifferent from a next frame.

In some cases compressed video is streamed and recorded in real time.When recording starts, the recording system begins capturing video dataincluding audio if any is present. A problem occurs in many cases whereno key frame (i-frame) has been captured at the beginning of therecording process. As a result, the beginning of the recorded videocannot be rendered correctly because it is missing the full video datasupplied by the key frame until the key frame arrives and is recorded.The delay in receiving a key frame may be as much as a few seconds whereaudio is heard but the video is blank or does not display correctly.

The inventor is aware of some proposed solutions to this problem such assnipping the first part of the video stream before the first key framearrives. The audio must be snipped as well to preserve synchronizationbetween the video and audio. A protocol has been proposed (IETF RFC5168) that enables a recording system to request that a key frame besent first by the device generating the video. A problem with thissolution is that the sender of the video must implement the protocol,which is not supported by most of the recording systems.

Therefore, what is clearly needed is a system and method for recordingcompressed video streamed live that solves the problems mentioned above.

SUMMARY OF THE INVENTION

The problem stated above is that when recording a live video and audiostream the first portion of the recording has insufficient video databecause only delta frames arrive at the recording system before a firstkey frame, which holds most of the video data. Known means foraddressing this issue have had undesirable side effects.

The inventors therefore considered functional elements of a datarecording system looking for elements that that could potentially beharnessed to provide a universally supported method for providingsufficient video data at the beginning of a video stream but in a mannerthat would not create drag redundancy or new requirements for protocoladoption.

The present inventor realized in an inventive moment that if, at thepoint of recording, a key video frame could be made available to arecording system at the beginning of the recording process, significantimprovement in quality of the initial portion of a recorded video andaudio stream might result. The inventor therefore constructed a uniquevideo recording system for real time recording of live video and audiothat allowed rich video data to be made available at the beginning ofthe stream before recording has started. A significant qualityimprovement results at playback of the recorded video and audio stream.

Accordingly, in an embodiment of the present invention, a system forrecording a compressed video-audio stream is provided and includes adecoder for decoding the video and audio packets of the stream, amultimedia recorder for recording the video and audio portions of thestream, and a video frame editor. In one embodiment the multimediarecorder receives and ignores initial delta frames of the video portionof the stream while buffering the audio portion of the stream receiveduntil a first key frame arrives and is buffered and decoded and whereinupon receiving a command to record, the system writes a copy of the keyframe at a predefined interval the first interval corresponding with thestart of the recording of the audio portion of the stream, the writeinterval repeated until a next key frame arrives whereby the video andaudio is then recorded as received.

In one embodiment the system is used for capturing voice mail messagesfrom network users. In another embodiment the system is used forcapturing interactive voice and video responses from an internetprotocol-based interactive voice response system enhanced for video. Inone embodiment the audio stream is decoupled from the video stream andbuffered for some period of time before the first video key framearrives. In one embodiment the delta frames are predicted (P) frames andthe key frame is an intra (I) frame. In another embodiment the deltaframes include bidirectional (B) frames.

According to another embodiment of the present invention in a system forrecording a compressed video-audio stream, a method for providing keyframe data at the beginning of a recording of the video-audio stream isprovided and includes the steps (a) receiving video and audio packets ofthe video-audio stream and buffering the audio data, (b) receiving,decoding, and buffering a first key frame received of the video portionof the video-audio stream, and (c) upon receiving a command to record,writing a copy of the first key frame at a predefined interval the firstinterval corresponding to the beginning of the audio stream.

In one aspect of the method in step (a) the audio stream is decoupledfrom the video stream. In one aspect the delta frames include predicted(P) frames. In one aspect the delta frames include bidirectional (B)frames. In one aspect in step (b) the key frame is an intra (I) frame.

According to another embodiment of the present invention, a system isprovided for recording a compressed video and audio stream. The systemincludes a decoder for decoding the video and audio stream, a multimediarecorder for capturing the video and audio portions of the stream, and avideo frame editor. In one embodiment the multimedia recorder delayswriting of the video data until a first key frame arrives, which uponreceiving a command to record, is reassigned by way of the video frameeditor as a starting key frame for the video stream corresponding to thebeginning of the audio stream and wherein delta frames reflecting zerochange of video content are generated by the video frame editor tofollow the key frame at predefined intervals from the starting key frameuntil the next key frame arrives.

In one embodiment the system is used for capturing voice mail messagesfrom network users. The system is used for capturing interactive voiceand video responses from an internet protocol-based interactive voiceresponse system enhanced for video. In one embodiment the audio streamis decoupled from the video stream and buffered for some period of timebefore the first video key frame arrives.

In one embodiment the delta frames are predicted (P) frames and the keyframe is an intra (I) frame. In one embodiment the delta frames includebidirectional (B) frames. In another embodiment a next key framearriving is replaced by a zero change delta frame.

According to another embodiment of the invention in a system forrecording a compressed video-audio stream, a method for providing keyframe data at the beginning of a recording of the video-audio stream isprovided and includes the steps (a) receiving video and audio packets ofthe video-audio stream and buffering the audio data, (b) receiving,decoding, and buffering a first key frame received of the video portionof the video-audio stream, (c) upon receiving a command to record,reassigning the first key frame received as a starting key frame for thevideo stream corresponding to the beginning of the audio stream, and (d)generating delta frames reflecting zero change of video content andwriting the delta frames following the key frame at predefined intervalsuntil the next key frame arrives. In one embodiment the audio stream isdecoupled from the video stream.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a network overview of a system for recording live video andaudio according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating video and audio recording andediting components according to an embodiment of the present invention.

FIG. 3 is a process flow chart illustrating steps 300 for recording acompressed live video-audio stream according to an embodiment of thepresent invention.

FIG. 4 is a process flow chart illustrating steps 400 for recording acompressed live video-audio stream according to another embodiment ofthe present invention.

FIG. 5 is a network overview of a system for recording live video andaudio according to another embodiment of the present invention.

DETAILED DESCRIPTION

The inventors provide a system and methods for real time recording of acompressed live video or video-audio stream that allows the recordedvideo to be played back correctly from the very beginning of therecording. The present invention is described in enabling detail belowaccording to the following examples, which may represent one or moreembodiments of the present invention.

FIG. 1 is a network overview of a system 113 for recording live video orvideo-audio according to an embodiment of the present invention. Acommunications network 100 is illustrated in this example and includes alocal public switched telephone network (PSTN) segment 101, a local PSTNsegment 102, and a wide-area-network (WAN) 103, which is alsorepresented herein by a WAN backbone 104. In one embodiment WAN 103 is aprivate or corporate WAN. In one embodiment of the invention, WAN 103 isthe Internet network. In this embodiment backbone 104 represents all ofthe lines, equipment, and access points that make up the Internetnetwork as a whole including connected sub-networks. Therefore, thereare no geographic limitations on practicing the present invention.

One example where real time recording of video-audio streams may occuraccording to an embodiment of the present invention is in a voice mailserver (VMS) such as VMS 113. VMS 113 is adapted with an accessibledigital storage medium to store software (SW) and data and to executemail applications relevant to serving recorded voice mail messages toclients of the server. VMS 113 has connection to WAN backbone 104 fornetwork access by client devices adapted to receive video mail.

A user 105 operating a personal computer 108 is illustrated within PSTNsegment 101 and represents a client of server 113 that may send orreceive video mails. User 105 has a headset 107 adapted with amicrophone for generating the audio portion of a video-audio stream thatcomprises a video mail. A camera 106 is illustrated in this example andis adapted to generate the video portion of the video-audio stream.

A user 109 operating a personal computer 112 is illustrated within PSTNsegment 102 and represents a client of server 113 that may send andreceive video mails. User 109 has a headset 111 adapted with amicrophone for generating the audio portion of a video-audio stream thatcomprises a video mail. A camera 106 is illustrated in this example andis adapted to generate the video portion of the video-audio stream.

It is noted herein that client software (SW) such as a mail programenhanced for video mail is presumed installed on both computers 108 and112. Computers 108 and 112 may be enhanced for video telephony using theappropriate client SW which is widely available. In one embodiment users105 and user 109 may operate dedicated video telephones instead ofpersonal computers enhanced for video mail and or video telephony.

Computer 108 and computer 112 are connected to WAN backbone 104 bynetwork access lines, typically through a network service provider likean Internet service provider (ISP) in the case of the Internet. User 105or user 109 may initiate a video-audio stream, which is uploaded tonetwork 103 and ultimately to VMS 113. VMS 113 contains video mailrecording software (SW) 114, which is provided for the purpose ofrecording video mails initiated by clients of the service. It ispresumed in this example that the system enables compression of the livevideo-audio using a standard format such as MPEG.

SW 114 allows the system to record live message streams for laterplacement in appropriate inbox destinations of an intended recipient(s).Without the system of the invention video mails played back byrecipients contain a black or blank video display while the first fewseconds of audio are heard. When a first key frame is played by theplayback SW or device, the video is then viewable and the audio issynchronized with the rest of the video. Recording SW 114 is enhancedwith a capability of recording a live compressed video-audio stream toenable a full video screen shot of the sender in the very first videoframe recorded. SW 114 is enabled by a built in algorithm that allows adelay in writing of the video data during the recording process until akey frame arrives to provide the rich video data required to support afull multimedia view of the sender of the video mail.

The system of the invention is not limited to implementation in a videomail application. The system of the invention can be practiced in anysystem that records live compressed video streams or video-audiostreams. More detail about the recording system of the present inventionis provided further below.

FIG. 2 is a block diagram illustrating video and audio recording andediting components of VMS 113 according to an embodiment of the presentinvention. VMS 113 accepts live compressed video-audio streams 200 fromclients of the system through an input/output (I/O) port 201. SW 114includes a video-audio decoder 203 for decoding the compressedvideo-audio data. In one embodiment of the present invention video-audiodata incoming through port 201 is first decoded by SW 114 decoder 203.Decoded video and audio data may then be buffered in a data buffer 202.Decoder 203 may be adapted to work with many different codecs.Decryption may also be a part of the decoding process.

In this example video data received as delta frames are ignored and arenot buffered in data buffer 202 prior to recording until a key framearrives that holds all of the video data supporting a full multimediaview of the sender of the video mail stream. Video frame editor 204 ispart of SW 114 and is adapted to enable copying of video data from afirst key frame arriving at the recording system. The copied key framedata may be rendered a series of key frames corresponding generally tothe ignored delta frames of the video stream. Video frame editor 204 mayalso enable video frame header manipulation for the purpose of alteringor removing time stamp information and other data typically found invideo frame headers.

Video frame editor 204 provides a copy of the first received key framecaptured from the video stream in order to reflect the full video datain the first frame and in subsequent frames before a next key frame ofthe video stream arrives. In this way all of the video data held in thefirst key frame is visible at the beginning of the audio data afterrecording has started. Only the first key frame of the video stream isbuffered and decoded. In this embodiment all delta frames received priorto the first key frame of the video stream are completely ignored by thesystem. After multimedia recording has started and a next real key framearrives, further frames of the video-audio stream (video and audio) aredecoded and recorded as received without a requirement for buffering thedata. In a preferred embodiment audio data received before the firstvideo key frame is buffered so that when multimedia recording starts,the audio and manipulated video are in sync with one another.

In another embodiment of the present invention video frame editor 204 isenhanced to assign the first key frame received and decoded as the firstframe of the recording. In this embodiment the delta frames receivedbefore the first key frame are ignored and delta frames reflecting zerochange in video content are generated to follow the starting key frameat predefined intervals consistent with the standard frame intervals ofa video stream. The interval period may vary somewhat according to userpreference as long as each frame causes the full video data in thestarting key frame to be displayed for the receiver of the video mailmessage. This effect is essentially the same as the first embodimentexcept that the key-frame need not be repeated at subsequent frameintervals until a next key frame arrives. In a variation to thisembodiment the next key frame that arrives may be replaced with a zerochange delta frame.

In one embodiment video data (first key frame) received at I/O port 201is buffered before decoding and recording. In another embodiment thedata is first decoded and then buffered. It is noted that in a preferredembodiment any delta frames received by the recording system from thevideo stream before the first key frame has arrived are ignored and notdecoded or buffered. The system looks for the first key frame of thestream, which has the rich video content required to fill a videodisplay.

Recorded video-audio files comprising Video mails in this example may bestored internally or externally in a storage medium 206. Storage medium206 may represent the storage space allotted to clients for mailstorage. Video mail files are served, in this case, through output port201 upon request (download). In one embodiment the mail server is aninstant message application protocol (IMAP) server where clients accessthe server to view mail but do not utilize a desktop application todownload content.

SW 114 including components 203-205 may be provided to other types ofvideo-audio enabled systems without departing from the spirit and scopeof the present invention. The illustration of a video mail server as arecording system in this example is exemplary only and is not to beviewed as a limitation of the present invention. The recording systemmay be an internet protocol (IP) based interactive voice response (IVR)system that records interactions for quality management and historicalarchiving. The present invention may be used unmodified in an IVR systemor in a video conferencing system without departing from the spirit andscope of the present invention. The present invention may be implementedunmodified in any instant messaging (IM) application that supports livevideo/voice interaction.

FIG. 3 is a process flow chart illustrating steps 300 for recording acompressed live video-audio stream according to an embodiment of thepresent invention. At step 301 a video-audio stream is received by avideo-audio recording system. The system may be a video mail server, anIP-IVR platform, or some other system enhanced for recording live videoand audio.

Video and audio of the stream may be decoded at step 302. Decoded deltaframes may be ignored and may not be buffered in a preferred embodiment.At step 303 the system buffers the audio data received and in thisexample ignores any video data that is not the first key frame of thevideo portion of the stream. At step 304 the system determines if it hasreceived a key frame associated with the video-audio stream beingbuffered. If the system has not received a key frame at step 304, theprocess loops back to step 303 continuing to buffer incoming audio data.

If the system determines a key frame has arrived in step 304, it isdecoded, buffered, and copied at step 305. The system may not buffer anymore data from the stream for any appreciable amount of time after theinitial key frame of the incoming stream has been detected. It ispresumed in this example that a record command is received at some pointbefore actual multimedia recording begins. This command is illustratedat left of process step 306. The system, upon receiving the commandrecord, may write the key frame copied at step 305 at specifiedintervals corresponding to the beginning of the audio stream at step 306while recording commences. Subsequent audio and video data receivedafter the first key frame can be decoded and forwarded directly to themultimedia recorder for recording in real time without being bufferedfor any length of time although buffering the data temporarily beforerecording may be an option without departing from the spirit and scopeof the present invention.

FIG. 4 is a process flow chart illustrating steps 400 for recording acompressed live video-audio stream according to another embodiment ofthe present invention. At step 401 a video-audio stream is received by avideo-audio recording system. The system may be a video mail server, anIP-IVR platform, or some other system enhanced for recording live videoand audio as described further above.

Video and audio of the stream is decoded at step 402. At step 403 thesystem buffers the audio packets received and ignores the initial videopackets received until the first key frame arrives. At step 404 thesystem determines if it has received a key frame associated with thevideo-audio stream being buffered. If the system has not received a keyframe at step 404, the process loops back to step 403 continuing tobuffer incoming audio data.

If the system detects the first received key frame at step 404, then thekey frame is decoded, buffered, and assigned as the starting frame ofthe video portion of the audio-video stream at step 405. The frame maybe assigned as the starting frame using the video frame editor. In thiscase key frame does not require any reproduction. At some point thesystem may receive a command to record the video-audio stream. Thiscommand is illustrated at the left of process step 405. At step 406 thesystem aided by the video frame editor generates delta frames thatreflect a zero change from the now starting key frame. In a variation ofthis embodiment the next key frame that arrives may also be replaced bya zero-change delta frame. Subsequent video frames received can bedecoded and forwarded directly to the multimedia recorder for recording.

In one embodiment of the present invention for both processes of FIG. 3and of FIG. 4, the initial video packets received are decoded andbuffered along with the first audio frames. In this case for the processof FIG. 3 the copied key frame data is inserted into the buffered deltaframes making them key frames. For the process of FIG. 4, the initialkey frame is made the starting frame and the buffered delta frames areedited to reflect a zero change from the new start frame.

The options of replicating a key frame at specified intervals or offilling in the buffered delta frames with the key frame data (FIG. 3)are interchangeable and may be performed automatically in real time asrecording commences. The only requirement is that the key frame hasarrived before recording begins. The command to record may be a defaultstep in the process depending on the use case scenario. The options ofgenerating new delta frames to reflect a zero change in video contentbehind a key frame that is assigned as a starting key frame or editingthe buffered delta frames to follow the new starting frame as zerochange frames depending on the starting key frame for data areinterchangeable and may be performed automatically in real time asrecording commences. A preference for replacing the initial delta framesignored by the system or editing those frames according to newrequirements may depend on the efficiency of those processes. Suchpreferences may vary from system to system in different embodiments.

It is noted herein as well that transmission of audio and video data ofa video-audio stream may be conducted over an IP-based network usingdata packetizing techniques known in the art wherein the video framesare reconstructed at the receiving end. In some cases the framestructure of the video stream may be preserved during transport of thestream over a supporting network.

FIG. 5 is a network overview of a system for recording live video andaudio according to another embodiment of the present invention. User 109and user 105 are illustrated in this example operating personalcomputers 112 and 108 respectively. User 109 is wearing headset 111 andusing video camera 110 while user 105 is wearing headset 107 and usingvideo camera 106. Both users' personal computers are connected to anInternet Protocol (IP) network illustrated herein by a network backbone501. Backbone 501 is an Internet network backbone in one embodiment. Inthis embodiment backbone 501 represents all of the lines, equipment andaccess points making up the Internet network as a whole. Therefore thereare no geographic limits to the practice of the invention in an IP-basednetwork environment. It is noted herein that video and audio data ispacketized for transport over an IP network using realtime transportprotocol (RTP) or a similar transport protocol suitable for livestreaming video-audio. In one embodiment network 501 is a LAN connectedto an Internet network and enhanced for transfer control protocol overInternet protocol (TCP/IP).

An IP-based IVR system or platform 500 is provided on network 501 and isadapted to interact with video/voice callers represented by users 105and 109. System 500 has a digital medium accessible thereto for storingvoice applications and for storing an executable version of IVRrecording software (SW) 502. SW 502 is adapted to record live compressedvideo and audio from users interacting with the system such as user 105and user 109. In one embodiment recorded interactions between users andthe system are forwarded to a universal contact server (UCS) 503connected to the network. UCS 503 is adapted to monitor and archiverecords of interaction including recordings made at IVR 500 using SW502. SW 502 is analogous to SW 114 described in FIG. 1 and FIG. 2.

UCS 503 may be connected directly to IVR system 500 in one embodimentand SW 502 may reside on UCS 503. UCS 503 has a data connection to a UCSdatabase 504 adapted for storing recorded interactions includingrecorded video and audio interactions made using SW 502. The recordingsystem of the present invention may be implemented at any network-basedend point system that records live compressed video or video-audiostreams. In one embodiment of the present invention the recording systemis implemented in an IP-based IVR system. In another embodiment therecording system is implemented in a video mail system. In anotherembodiment the recording system is implemented in a video conferencebridge system. In still another embodiment the system is implemented ina contact server that monitors live interactions.

In a preferred embodiment to minimize buffering requirements all initialdelta frames of the video portion of the video-audio stream are ignoredby the recording system while the audio is buffered. In this case onlythe first video key frame that contains the rich video data required tofill the display is buffered. Key frame replication or key framereassignment followed by delta frame generation occurs in real timeafter recording is undertaken by the system. In both embodiments when anext key frame is received by the recording system the subsequent videoand audio data received may be recorded in real time without reliance onbuffering or any video frame editing. However, there may be someembodiments where buffering of all of the incoming data is performed bydefault even after the second key frame is received by the system andrecording has started.

It will be apparent to one with skill in the art that the recordingsystem of the invention may be provided using some or all of thementioned features and components without departing from the spirit andscope of the present invention. It will also be apparent to the skilledartisan that the embodiments described above are specific examples of asingle broader invention which may have greater scope than any of thesingular descriptions taught. There may be many alterations made in thedescriptions without departing from the spirit and scope of the presentinvention.

1. A system for recording a compressed video-audio stream comprising: adecoder for decoding the video and audio packets of the stream; amultimedia recorder for recording the video and audio portions of thestream; and a video frame editor; characterized in that the multimediarecorder receives and ignores initial delta frames of the video portionof the stream while buffering the audio portion of the stream receiveduntil a first key frame arrives and is buffered and decoded and whereinupon receiving a command to record, the system writes a copy of the keyframe at a predefined interval the first interval corresponding with thestart of the recording of the audio portion of the stream, the writeinterval repeated successively until a next key frame arrives wherebythe video and audio is then recorded as received.
 2. The system of claim1 used for capturing voice mail messages from network users.
 3. Thesystem of claim 1 used for capturing interactive voice and videoresponses from an internet protocol-based interactive voice responsesystem enhanced for video.
 4. The system of claim 1 wherein the audiostream is decoupled from the video stream and buffered for some periodof time before the first video key frame arrives.
 5. The system of claim1 wherein the delta frames are predicted (P) frames and the key frame isan intra (I) frame.
 6. The system of claim 1 wherein the delta framesinclude bidirectional (B) frames.
 7. In a system for recording acompressed video-audio stream, a method for providing key frame data atthe beginning of a recording of the video-audio stream comprising thesteps: (a) receiving video and audio packets of the video-audio streamand buffering the audio data; (b) receiving, decoding, and buffering afirst key frame received of the video portion of the video-audio stream;(c) upon receiving a command to record, writing a copy of the first keyframe at a predefined interval the first interval corresponding to thebeginning of the audio stream; and (d) recording the video and audiostream.
 8. The method of claim 7 wherein in step (a) the audio stream isdecoupled from the video stream.
 9. The method of claim 7 wherein thedelta frames include predicted (P) frames.
 10. The method of claim 7wherein the delta frames include bidirectional (B) frames.
 11. Themethod of claim 7 wherein in step (b) the key frame is an intra (I)frame.
 12. A system for recording a compressed video and audio streamcomprising: a decoder for decoding the video and audio stream; amultimedia recorder for capturing the video and audio portions of thestream; and a video frame editor; characterized in that the multimediarecorder delays writing of the video data until a first key framearrives, which upon receiving a command to record, is reassigned by wayof the video frame editor as a starting key frame for the video streamcorresponding to the beginning of the audio stream and wherein deltaframes reflecting zero change of video content are generated by thevideo frame editor to follow the key frame at predefined intervals fromthe starting key frame until the next key frame arrives.
 13. The systemof claim 12 used for capturing voice mail messages from network users.14. The system of claim 12 used for capturing interactive voice andvideo responses from an interne protocol-based interactive voiceresponse system enhanced for video.
 15. The system of claim 12 whereinthe audio stream is decoupled from the video stream and buffered forsome period of time before the first video key frame arrives.
 16. Thesystem of claim 12 wherein the delta frames are predicted (P) frames andthe key frame is an intra (I) frame.
 17. The system of claim 12 whereinthe delta frames include bidirectional (B) frames.
 18. The system ofclaim 12 wherein a next key frame arriving is replaced by a zero changedelta frame.
 19. (canceled)
 20. The method of claim 7 wherein in step(a) the audio stream is decoupled from the video stream.